1. Field of the Invention
This invention relates to an improved fuel injector system for use with internal combustion engines.
2. Description of the Prior Art
Stroke-controlled injection systems with a high-pressure accumulator are known and used to deliver fuel in direct-injecting internal combustion engines. The advantage of these injection systems lies in the fact that the injection pressure can be adapted to wide ranges of load and engine speed. A high injection pressure is required in order to reduce emissions and to achieve a high specific output. Since the achievable pressure level in high-pressure fuel pumps is limited for strength reasons, pressure boosters are used in the fuel injectors in order to further increase pressure in fuel injection systems.
Stroke-controlled injection systems with a high-pressure accumulator are used to deliver fuel in direct-injecting internal combustion engines. The advantage of these injection systems lies in the fact that the injection pressure can be adapted to wide ranges of load and engine speed. A high injection pressure is required in order to reduce emissions and to achieve a high specific output. Since the achievable pressure level in high-pressure fuel pumps is limited for strength reasons, pressure boosters are used in the fuel injectors in order to further increase pressure in fuel injection systems.
DE 101 23 913 relates to a fuel injection apparatus for internal combustion engines, having a fuel injector that can be supplied from a high-pressure fuel source. A pressure boosting device that has a movable pressure booster piston is connected between the fuel injector and the high-pressure fuel source. The pressure booster piston divides a chamber that can be connected to the high-pressure fuel source from a high-pressure chamber connected to the fuel injector. The fuel pressure in the high-pressure chamber can be varied by filling a return chamber of the pressure boosting device with fuel or by emptying fuel from this chamber. The fuel injector has a movable closing piston for opening and closing injection openings. The closing piston protrudes into a closing pressure chamber so that fuel pressure can be exerted on the closing piston in order to produce a force that acts on the closing piston in the closing direction. The closing pressure chamber and the return chamber are constituted by a combined closing pressure/return chamber, all of the partial regions of the closing pressure/return chamber being permanently connected to one another to permit the exchange of fuel. A pressure chamber is provided for supplying fuel to the injection openings and for exerting a force on the closing piston in the opening direction. A high-pressure chamber is connected to the high-pressure fuel source so that aside from pressure fluctuations, at least the fuel pressure in the high-pressure fuel source can continuously prevail in the high-pressure chamber. The pressure chamber and the high pressure chamber are constituted by a combined injection chamber, all of the partial regions of the injection chamber being permanently connected to one another to permit the exchange of fuel.
DE 102 294 18.6 relates to a fuel injection apparatus for injecting fuel into the combustion chamber of an internal combustion engine. The fuel injection apparatus includes a high-pressure source, a pressure booster, and a metering valve. The pressure booster has a working chamber and a control chamber that are separated from each other by a piston; a pressure change in the control chamber of the pressure booster causes a pressure change in a compression chamber. Via a fuel inlet, the compression chamber acts on a nozzle chamber encompassing an injection valve member. A nozzle control chamber that acts on the injection valve member can be filled on the high-pressure side from the compression region via a line containing an inlet throttle restriction and can also be connected on the outlet side to a chamber of the pressure booster via a line containing an outlet throttle restriction.
The metering valve according to the above-described design is embodied in the form of a 3/2-way valve that controls a large return flow quantity occurring in this pressure booster-equipped design. Although embodying the metering valve in the form of a 3/2-way servo-valve does achieve a simplified, inexpensive manufacture, it is disadvantageous that a leakage gap forms between the control chamber of the servo-piston of the servo-valve and a return line when the fuel injector is idle. The actuation fluid flowing out through the leakage gap decreases the efficiency of the system and requires that the sealing gap be provided with a long guidance length. A long guidance length of the sealing gap in turn requires a long structural length of the valve body of the servo-valve, which is undesirable in terms of available installation space since the aim is to produce a fuel injector that has an integrated pressure booster and is as compact as possible.